In modern megavoltage (MV) X-ray radiation therapy, the radiation detector used to determine the position of the patient within the therapy system is typically different from the detector used to measure the radiation dose delivered to that patient during the therapy session. One reason that two separate detectors are used is that the sensitivity of the detector for anatomical imaging is different from the sensitivity of the detector for measuring radiation dosage. Detectors suitable for anatomical imaging, such as electronic portal imaging detectors (EPID), often use scintillating materials made of heavy elements, such as Gadolinium oxysulfide (GOS) or cesium iodide doped with thallium (CsI(Tl)). However, because such materials have a radiation dose response which is vastly different from tissue or water, they are not suitable for patient dosimetry measurements. Detectors suitable for measuring the radiation dose delivered to a patient are typically made of a low-Z material, which have a similar radiation dose response to that of tissue or water. Examples may include dry air in ion chambers, diamond, silicon, etc. Such detectors are not appropriate for acquiring images because of their low stopping power for X-rays. Although increasing the thickness of the low-Z material may allow for the capture of more X-rays, the resultant image may have poor spatial resolution.
Accordingly, a radiation detection system that is capable of both acquiring images at a useful spatial resolution and measuring the radiation dose delivered to a patient is desirable.